The Thermo Cube is a unique, patented electrical device that plugs into a standard 15 amp electrical outlet and turns power on automatically according to outside air temperature, saving money by using power only when temperatures require heating or cooling. There are five models available with different temperature ranges to choose from. Each unit has two receptacles for use with more than one electrical device. Warm weather model TC-21 turns on at 78°F, off at 70°F and is ideal for all types of home and farm fans: window, ceiling, exhaust, ventilators, attic and roof. Also industrial ceiling, room, air circulator and table fans. One year limited warranty.